There are some really good questions and answers here. In P1, P2 and AVPR, they didn't wear nearly as much armor as in AVP. I favor the notion that the younglings on their first hunt are outfitted with inferior armor and blades to make it more challenging. Wolf's blades were acid resistant because he used them on an alien in the hospital hive and also put them through Chet's skull and they showed no signs of melting. Also, the armor could be specific to the clan that uses Earth as a training ground, and not the whole race. Each clan would have their specific history and customs, so why not different armor. The different facial appearance of the AVP Preds could be another slight difference between clans that have been seperated for a long time. If you stop and think about it, NONE of the Predators we've seen were identical in appearance. Scar's clan all had the same facial appearance and the longer dreads, but they looked different from all the other Preds in the other movies. I know as far as the moviemakers go, it's just because the costuming and makeup has evolved since the '80s and they just want their own version of the Pred, but it still is an interesting theory. Anytime had the simplest facial appearance, being the first Predator, and the design has been tweaked in every successive film. The stagnation question is really strange to start with, given the fact that we've only seen a microscopic part of the Pred society. We don't have nearly enough information about them to even ask that question. We really need some GOOD Pred films to explore their universe a little at a time. There are so many possibilities for future Pred films if the right people will just stand up and make them. Look at mankind here on Earth, and think how much older and more complex the Pred society must be. It would take a dozen films to get a good idea of what they're really like on different levels. Hopefully the people at Fox will wake up one day and start monitoring this board. There are far better ideas thrown around here than in the whole of Hollywood I think.
That's why I'd love to see a bad-blood film. To see Preds going head-to-head would be fantastic! I'd love to see a bad-assed rogue hunted by several other bad-asses who all go down strong until the final battle between the bad-blood and the best arbitrator sent after him. The arbitrator wins and survives, taking the bad-blood or his corpse home with him for whatever ritual or punishment is appropriate. The arbitrator would have to be the toughest and smartest Pred we've seen so far, but the bad-blood would have to match him for the most part. An elder like Broken Tusk as the arbitrator would be great. If they have to put humans in it, make them ADULT scientists or something who are just watching the story play out and not becoming involved. Trapped in the middle and ignored by the Preds as they fight each other on an alien world, but definitely not on Earth! Maybe they could collect one of the dead Preds after his fight with the bad-blood and study him. That would be a great opportunity to learn a little more about the Pred physiology itself. In a perfect world...